Be used for standard specimen of thermogravimetric analyzer temperature calibration and preparation method thereof
Technical field
The present invention relates to a kind of standard specimen that is used for the thermogravimetric analyzer temperature calibration and preparation method thereof, specifically, relate to the standard specimen product that utilizes sol-gel process to prepare the demarcation temperature that thermogravimetric analyzer uses, belong to the standard substance field.
Background technology
Thermogravimetric analyzer is the most frequently used thermal-analysis instrumentation, and its quantitative property is strong, can be widely used in fields such as physics, chemistry, material, we can say, as long as material is when being heated, the variation of weight takes place, and all can study its change procedure with thermogravimetry (TG).Using thermogravimetric analysis (TG) when instrument is tested, the correction of temperature is crucial, the verification temperature has following three kinds of methods at present: the one, adopt to indicate the standard substance that temperature has the weightless point of reproduction again, it is not only relevant with temperature that yet product is overflowed, also relevant with heating rate, this is the limitation of this method.The 2nd, adopt to have and can reproduce or the material of reversible inversion temperature, the characteristics of this method are irrelevant with atmosphere, it requires, and thermopair contacts with sample or supporter in checking procedure, the material that can use as standard is that those have the material that the solid or solid liquid of solid changes, as potassium nitrate, potassium chromate and tin etc.The 3rd, adopt to have fixed temperature and issue magnetisation variation and can be the material of this reacting condition on the TG curve.This class material is magnetic alloy or metal normally, as nickel, iron, etc.Be placed on magnetic material in the supporter and make it to be in the magnetic field, when temperature rises when reaching the Curie point of material in the supporter, magnetic force disappears, and thermobalance indicates the apparent loss in weight with the magnetic force equivalence.
Desirable standard ferromagnetic material should have following character:
1) the magnetic transformation process must that is to say just to become magnetic to change in very little temperature range rapidly.Can obtain steep TG curve like this.The interval big or small dTc of general available magnetic sample transition temperature characterizes the definite precision of standard specimen to instrument temperature.The concrete practice is: does magnetic thermogravimetric curve differential curve, a peak value can occur at magnetic transition point, and the corresponding magnetic transition temperature variation of the halfwidth dTc at this peak interval, the more little precision of dTc is big more.
2) it is little to cause that magnetic changes needed externally-applied magnetic field.
3) the magnetic transformation temperature is not influenced by the chemical attribute of atmosphere should, should be irrelevant with atmosphere pressures.
4) the magnetic change procedure should be reversible so that sample can repetition test, up to temperature correction till the optimum value.
5) the magnetic change procedure should not be subjected to the influence of other reference material, to guarantee testing several samples simultaneously.
6) the standard model amount can be observed change procedure significantly in the milligram level.
The now domestic and international used standard specimen of thermogravimetric analyzer, mainly provide by two external big instrument companies, the one, Germany anti-executing (NETZSCH) company, its standard specimen that provides is feeromagnetic metal or alloy, the disk shape, to between the 200mg, the scale temperature is respectively 74 ℃, 160 ℃, 266 ℃, 358 ℃, 497 ℃, 770 ℃ to every tablet quality at 80mg, about 200 marks of each standard specimen price (closing 1200 yuan of Renminbi).Another is a U.S. PERKIN-ELMER company, and its standard specimen also is nickel, iron and other magnetic alloy, and it is thread or banded that standard specimen mostly is, and the verification temperature is respectively 163 ℃, 354 ℃, and 438 ℃, 596 ℃, 780 ℃, 1000 ℃.Metal or alloy standard specimen environmental requirement to external world is harsh, and apt to deteriorate in acid atmosphere or wet environment, sample retention is strict.The main following points of defective of Germany and U.S.'s standard specimen: the one, lack near the standard model of room temperature, the 2nd, the metal standard specimen is easy to corrosion under the environment of high humidity, and the 3rd, sample is a not acid-alkali-corrosive-resisting of metal, the 4th, precision is not very good.
Summary of the invention
The object of the present invention is to provide a kind of simple and effective standard specimen that is used for the thermogravimetric analyzer temperature calibration and preparation method thereof, standard specimen verification temperature is respectively near the room temperature and near 90 ℃, acid-alkali-corrosive-resisting, apparent thermogravimetric change (highly) amount greatly, and low price.
The present invention adopts the magnetic rare earth oxide ceramic with giant magnetoresistance effect to be ready for use on the standard specimen of thermogravimetric analyzer temperature calibration, and the percentage by weight of its component is respectively
La 42~48;
Sr 7~12;
Mn 22~25;
O 20~22。
The main technique flow process of preparation standard specimen is as follows:
Take by weighing the La of doses by above-mentioned standard specimen component ratio
2O
3Be dissolved in HNO
3Get colourless transparent solution, take by weighing Mn (CH
3COO)
24H
2The water-soluble one-tenth colourless transparent solution of O takes by weighing Sr (CH
3COO)
2H
2O is dissolved in H
2O becomes colourless transparent solution, then above-mentioned three kinds of solution are mixed, add citric acid again in the mixed liquor and make peptizator, magnetic agitation 3 hours, keeping temperature of reaction is 60 ℃. then with the mixed liquor evaporate to dryness, get the loose powder of black, again powder was placed 1000 ℃ of sintering of muffle furnace 2 hours, obtain nanocrystalline powder; Above-mentioned nanometer crystal powder is pressed into disk by the standard specimen requirement,, promptly obtains being used for the ceramic standard specimen of thermogravimetric analyzer temperature calibration 1200 ℃ of sintering 5 hours.The Curie point that is prepared into standard specimen is at 29 ℃ and 90.4 ℃.
It is as follows that standard specimen is used for the concrete operations of thermogravimetric analyzer temperature calibration verification: at the thermogravimetric analyzer initial period, above-mentioned standard specimen is placed in the analyser thermobalance, add low-intensity magnetic field (intensity is 100 Gausses), heat up then, above-mentioned sample has apparent weight sudden change at Curie point, writes down instrument displays temperature this moment, compares with the Tc point of standard specimen itself, again instrument is carried out the temperature adjustment, till the standard temperature scope.The storage of standard specimen is that the product of making is contained in the plastic sample box, and the time spent is not put into exsiccator.
We compare with external standard specimen, and advantage exists: 1) fill up near domestic and international standard specimen blank of (29 ℃) room temperature.2) our standard specimen weight is less than 1/5th of German standard specimen, and apparent thermogravimetric changes and surpasses German product, and consumption few (more than 30 milligrams) is quick on the draw.3) temperature accuracy of our two samples is respectively 6.8 ℃ and 5 ℃, Germany be 19.1 ℃ and 7 ℃, our product precision is wanted high .4) our sample is ceramic sample, acid-alkali-corrosive-resisting, Germany and U.S.'s sample are metal or alloy, the fearness acid and alkali corrosion.4) adopt the oxide magnetic pottery to do standard specimen first, rather than magnetic metal or alloy.5) we prepare sample and adopt simple sol-gel technique, sample constituents is evenly adjustable, about 1200 ℃ of sintering temperatures, standard specimens such as Germany must be mixing with the metal congruent melting, about 2600 ℃ of sintering temperatures, our sample price is 500 yuan/kilogram, Germany's product price is 600,000/kilogram, and price is our 10,000 2000 times, in view of this, our standard specimen technology is easy, low price.
Description of drawings
Fig. 1 is the magnetic thermogravimetric curve of standard specimen of the present invention.
Fig. 2 is the magnetic thermogravimetric curve of the anti-company's standard specimen of speeding of Germany.
Among Fig. 1, we utilize magnetic rare earth oxide pottery with giant magnetoresistance effect to prepare the disk shape pottery of Curie point 29 ℃ and 90.4 ℃, sample shape is Φ 5 * 1mm quality for being respectively 33mg, 30mg, and the anti-weight of speeding company's standard specimen of Germany is our more than 5 times of sample.
Among Fig. 2, by the TG curve as can be seen, the dTc value of this standard specimen is respectively 19.1 ℃ and 7 ℃, and the dTc value of two samples that we are prepared is respectively 6.8 ℃ and 5 ℃, and as seen our precision will be higher than German product.Comparison diagram 1 and Fig. 2 as can be seen, the apparent thermogravimetric of our sample changes the sample of (highly) amount greater than German company, and the sample of unit mass be described, our standard specimen consumption is few, changes obvious.On the other hand, take a broad view of the standard specimen of anti-speed company and U.S. P-E company of Germany, lack near the standard model of room temperature, and we have near the standard specimen of room temperature, and we adopt the magnetic ceramics of acid-alkali-corrosive-resisting to substitute magnetic metal for the first time or alloy is made standard specimen.
Embodiment
With La
0.8Sr
0.2MnO
3Standard specimen is an example, and its weight percentages of components is
La 47.98;
Sr 7.57;
Mn 23.72;
O 20.73。
Its preparation method is: used chemical reagent mainly contains: La
2O
3, Sr (CH
3COO)
2H
2O, Mn (CH
3COO)
24H
2O, dense HNO
3, citric acid, by La: Sr: Mn=8: 2: 10 mol ratio takes by weighing above-claimed cpd.Key step is as follows: the La that takes by weighing doses
2O
3Be dissolved in an amount of HNO
3Get colourless transparent solution, take by weighing Mn (CH
3COO)
24H
2O is dissolved in suitable quantity of water and becomes colourless transparent solution, takes by weighing Sr (CH
3COO)
2H
2O is dissolved in H
2O becomes colourless transparent solution, then above-mentioned three kinds of solution are mixed, the citric acid that adds doses in the mixed liquor is made peptizator again, magnetic agitation 3 hours, keeping temperature of reaction is 60 ℃. then with the mixed liquor evaporate to dryness, get the loose powder of black. again powder is placed 1000 ℃ of sintering of muffle furnace 2 hours, and obtained nanocrystalline La
0.8Sr
0.2MnO
3Powder. above-mentioned nanometer crystal powder is pressed into φ 5 * 1mm disk and φ 10 * 1mm disk,, promptly obtains La 1200 ℃ of sintering 5 hours
0.8Sr
0.2MnO
3Pottery.
La
0.7Sr
0.3MnO
3The weight percentages of components of standard specimen is
La 42.94;
Sr 11.61;
Mn 24.26;
O 21.19。
Its preparation process is the same, and only its mol ratio is La: Sr: Mn=7: 3: 10.